Certain kinds of pyrazole derivatives are already known to exhibit such physiological activities utilizable as agricultural chemicals. For instance, Japanese patent publication No. 19958/65 discloses that a class of N-phenylpyrazole derivatives represented by the formula ##STR2## wherein R.sub.1 is a hydrogen atom or phenyl group, R.sub.2 is a hydrogen atom or a (lower)alkyl group, R.sub.3 is a hydrogen atom, nitro group or cyano group and R.sub.4 is a (lower)alkyl group, amino group or a (lower)alkoxy group shows herbicidal activity. Besides, Japanese patent publication No. 14833/67 discloses that an N-(nitro-substituted phenyl) pyrazole derivative or an N-(chloro-nitro-substituted phenyl)pyrazole derivative represented by the general formula ##STR3## wherein X is Cl or H exhibits fungicidal activity and is useful to control fungicidal infections in crop-plants such as tomato, rice and kidney bean. Nonetheless, such N-phenylpyrazole derivatives of which the phenyl nucleus is bearing halogen atoms at the 2- and 4-positions and a hydroxy group or substituted hydroxy group at the 5-position in accordance with this invention, as be seen with the new compounds of this invention, have never been known before our invention, as far as we are aware of.
The known particular pyrazole derivatives according to the Japanese patent publication No. 19958/65 and No. 14833/67 can exhibit no or little herbicidal activity and are practically not useful as the herbicidal agent. Accordingly, we have made our researches in an attempt to provide such new pyrazole derivatives which show remarkably higher herbicidal activities than the above-mentioned known particular pyrazole derivatives, and which are practicably utilizable as the herbicidal agent for irrigated field of aquatic rice plant and also as the herbicidal agent for farm-fields (non-irrigated) for various kinds of crop-plants.